"She promised me she wouldn't get any bigger," Kim Kardashian West captioned an Instagram video of her daughter, who was wearing a PilyQ swimsuit. "I can't believe my baby girl is three years old today!!!! Northie, I love you so much. I can't even explain it! Happy Birthday to my favorite mermaid!!!

A video posted by Kim Kardashian West (@kimkardashian) on Jun 15, 2016 at 7:34am PDT

North's grandmother, Kris Jenner, also shared the video with a super sweet message. "Happy third birthday to my little angel, my precious granddaughter North!!!" the 60-year-old momager wrote. "I can’t believe you’re three today! You are growing into the most beautiful little girl!!! You bring us so much joy and I thank God every day for blessing us with you. I love you beyond words!"

A photo posted by Khloé (@khloekardashian) on Jun 15, 2016 at 9:54am PDT

Meanwhile, Kim went on to post a message for North on her website, along with some precious photos. "The joy of my world, my best friend -- I would be lost without you," the 35-year-old reality star wrote. "I've loved seeing you grow up, and I can't wait for many more amazing years. I love you, my bubs!"

North is definitely her mother's muse, and is frequently featured on Kim's Snapchat and Instagram. Check out some of the stylish toddler's most adorable moments above.